Printed multifunctional skin for aerodynamic structures, and associated systems and methods

ABSTRACT

Systems and methods for printed multifunctional skin are disclosed herein. In one embodiment, a method of manufacturing a smart device includes providing a structure, placing a sensor over an outer surface of the structure, and placing conductive traces over the outer surface of the structure. The conductive traces electrically connect the sensor to electronics.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/168,726, filed Oct. 23, 2018, which is a continuation of U.S.application Ser. No. 15/295,702, filed Oct. 17, 2016, which claims thebenefit of U.S. Provisional Application No. 62/242,492, filed Oct. 16,2015, the disclosures of which are hereby incorporated in theirentirety.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made with Government support under contract No.FA9550-15-C-0007 awarded by the U.S. Air Force ResearchLaboratory—Office of Scientific Research. The Government has certainrights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to sensors and actuatorsattached to the structures, including aircraft.

BACKGROUND

Conventional aircrafts may carry large numbers of sensors and actuators.For example, the aircrafts are typically equipped with instruments thatcan measure outside temperature, speed of the aircraft, outside/insidepressure, humidity, weight of the aircraft, etc. Some measurementsensors (e.g., inside humidity and temperature) and most of thesupporting electronics are typically installed inside the aircraft. Onthe other hand, other measurement sensors typically protrude outside ofthe aircraft (e.g., pitot tube for the pressure/speed measurements).Additionally, the aircrafts also carry actuators (e.g., for landing geardeployment and retraction, for wing flaps, ice protection systems,etc.). These actuators are generally bulky and, when not exercised, aretypically concealed within the aircraft. Some other sensing/actuationaerospace systems perform monitoring for the structures, ice protection,thermal management, vibration damping, etc.

However, the available space for the instruments and their supportingelectronics is generally reduced in the newer, smaller aircraft. Forexample, small drones may not have enough space to carry all theactuators and sensors, and the supporting electronics. Similar problemsexist with the newer manned aircraft, because those are also smaller atleast in part due to stronger materials used for these aircraft that, inturn, enable smaller aircraft.

Furthermore, additional instruments/sensors may measure, for example,loading of the aircraft structure, especially during the development ofthe aircraft (Testing and Evaluation or T&E). For example, strainsensors may be mounted on the load bearing parts of the aircraftstructure during the testing of the aircraft, but the productionaircraft would not include these strain sensors. Existing methods forassessment/management of the structural health, certification of flightreadiness and fleet management are largely based on statistical dataabout the history of the aircraft, and depend heavily on the expertiseof mechanics and engineers. Accordingly, there remains a need for thesensors and actuators that are compact, light, and inexpensive, and thatcan be used for the manned and unmanned aircraft.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic view of an aircraft equipped with sensors inaccordance with an embodiment of the presently disclosed technology.

FIG. 2 is an isometric view of an aircraft structure equipped withsensors and actuators in accordance with an embodiment of the presentlydisclosed technology.

FIG. 3 is a top plan view of a printed multifunctional skin (pSKIN)equipped with sensors and actuators in accordance with an embodiment ofthe presently disclosed technology.

FIGS. 4A-4C are isometric views of a pSKIN mounted on an aircraftstructure in accordance with an embodiment of the presently disclosedtechnology.

FIG. 5 is an exploded view of a pSKIN assembly in accordance with anembodiment of the presently disclosed technology.

FIGS. 6A and 6B are plan and isometric views of an aircraft with sensorsand actuators in accordance with an embodiment of the presentlydisclosed technology.

FIGS. 7A-7F are schematic views of equipping an aircraft structure withsensors and actuators in accordance with an embodiment of the presentlydisclosed technology.

FIG. 8 is an isometric view of printing sensors and actuators over anaircraft in accordance with an embodiment of the presently disclosedtechnology.

FIG. 9 is an isometric view of a wind tunnel testing of sensors andactuators in accordance with an embodiment of the presently disclosedtechnology.

FIGS. 10A and 10B are graphs of load measurements in accordance with anembodiment of the presently disclosed technology.

DETAILED DESCRIPTION

Specific details of several embodiments of representative sensors andactuators carried by aircraft, and associated methods of manufacturingand use are described below. The system and methods can be used forequipping the aircraft or an aerodynamic structure with the sensors,actuators, and the supporting electronics (also referred to as printedmultifunctional skin (pSKIN) or instrumentation), and for using theinstrumentation for developing, testing and using the aircraft or theaerodynamic structure.

In at least some embodiments, the sensors (pressure sensors, temperaturesensors, strain sensors, ice sensors, strain transducers, RF antennas,etc.) and actuators (e.g., heaters, ionic actuators, plasma actuators,miniature air blowers, etc.) may be built using 3D printing (alsoreferred to as 3D manufacturing, additive printing, additivemanufacturing, or direct write). The sensors and actuators may beprinted directly over the aircraft structures or inside relativelyshallow cavities of the aircraft structures. In some embodiments, thehost aircraft structures can also be made by 3D printing.

Furthermore, in at least some embodiments, the electronics may also beprinted using specialized 3D printing equipment, methods and materialsor “inks” (e.g., conductors, semiconductors, and dielectrics). Someexamples of 3D-printed electronic elements or components areinterconnects, electrodes, resistors, capacitors, and activeelectronics. As a result, a multifunctional, smart and lightweightdevice can be created.

In many embodiments, a relatively high density of sensors/actuators at areduced unit cost/weight is advantageous over the bulky legacy systems.For example, many sensors/actuators and their supporting electronics(e.g., microcontrollers, op-amps, analog to digital (A/D) converters,resistors, power supplies, etc.) can be 3D manufactured at the outersurface of the aircraft structure in conjunction with the manufacturingof the aircraft structure itself (as opposed to placing the conventionalsensors/actuators/electronics deeper inside the aircraft structure withthe conventional technology). In some embodiments, one or morerelatively shallow openings (e.g., 2-10 millimeter deep) in the aircraftstructure may house power supplies, electronics, connectors, etc., forthe sensors/actuators. Because of their relatively low height, thesensors/actuators closely approximate the surface of the aircraftstructure, therefore not impeding or disturbing the airflow around theaircraft structure. In some embodiments, the sensors/actuators may be 3Dprinted directly over the outer surface of the aircraft structure inconjunction with manufacturing of the aircraft structure itself, orafter the aircraft structure has been already manufactured.

In some embodiments of the inventive technology, the sensors/actuators,and the electronics may be printable onto a conforming foil (e.g., adecal, also referred to as pSKIN) that is subsequently transferred to anexisting aircraft structure. In some embodiments, the conforming foilsmay have thickness of several micrometers (e.g., less than 100 μm, or 5μm-100 μm) to several millimeters (e.g., 2-10 mm).

Data from the 3D-printed sensors may provide an assessment of the stateof the aircraft and/or an improved modeling (e.g., numerical simulation)of performance over time, therefore resulting in improved monitoring ofthe structure and better prediction of maintenance needs. In someembodiments, the inventive technology can enable a “Digital Twin,” whichis a mirror computer model of the aircraft that integrates numericalsimulation with data from aircraft sensors (e.g., 3D printed sensors),the aircraft maintenance history, and historical statistical data acrossaircraft of the same type to enable improved safety and reliability. Insome embodiments, the Digital Twin may be used to improve the models ofthe aircraft.

In some embodiments, the above-described methods and systems may beapplied to other structures, e.g., pumps, wind turbines, submarines,ships, engines, blades, prosthetics, pipelines, etc. For example, a vaneof an air fan may be equipped with 3D-manufactured sensors/actuators (apSKIN) at an outer surface of the vane for monitoring or optimization ofthe air fan's performance.

FIG. 1 is a schematic view of an aircraft 1000 equipped with sensors inaccordance with an embodiment of the presently disclosed technology. Theaircraft 1000 can carry 3D-printed pressure sensors 105, temperaturesensors 110, and/or strain sensors 115. These sensors may send theirmeasurement data to a local or a central processing/display unit (e.g.,a display in the airplane cockpit, computer carried by an unmannedvehicle, etc.). Other numbers and types of sensors are also possible. Insome embodiments, the aircraft 1000 may also carry 3D-printed actuators.

FIG. 2 is an isometric view of an aircraft structure 200 equipped withsensors and actuators in accordance with an embodiment of the presentlydisclosed technology. The illustrated aircraft structure 200 may be, forexample, a segment of an aircraft wing. In some embodiments, theaircraft structure 200 can include openings 255 for connecting with theadjacent aircraft structures. The aircraft structure 200 carries a decal(pSKIN) 280. The combination of the pSKIN 280 and the aircraft structure200 may be referred to as a smart structure or a smart device 2000. Theillustrated pSKIN 280 includes sensors 215 (e.g., strain sensors orstrain gauges) and actuators 220 (e.g., heaters), but othersensors/actuators are also possible. The sensors 215 and actuators 220are connected with conductive traces 230 to the connectors 225 (e.g.,metal pads or plugs). In at least some embodiments, the supportingelectronics (not shown) may be connected through the connectors 225 tothe sensors/actuators 215/220. In some embodiments, the supportingelectronics may be at least partially embodied in the pSKIN 280.Generally, the pSKIN 280 remains flexible because of its relativelysmall thickness (e.g., less than 10 μm to few mm). As a result, thepSKIN 280 may follow the shape of the aircraft structure 200, and may befolded over the edges of the aircraft structure 200. The pSKIN 280 canalso be directly printed over the aircraft structure 200.

FIG. 3 is a top plan view of a pSKIN 380 with sensors and actuators inaccordance with an embodiment of the presently disclosed technology. Inthe illustrated embodiment, the pSKIN 380 includes sensors 215 (e.g.,for temperature measurements), and an actuator 310 (e.g., a heater). Inother embodiments, the pSKIN 380 may include different type and numberof sensors/actuators and supporting electronics, only sensors, or onlyactuators. The sensors 215 and the actuator 310 are connected withconductive traces (e.g., metal traces) with the connectors 225.

FIGS. 4A-4C are isometric views of the pSKIN 380 mounted on an aircraftstructure in accordance with an embodiment of the presently disclosedtechnology. FIG. 4A shows the pSKIN 380 applied over the aircraftstructure (e.g., an airfoil or a segment of the aircraft wing) 200(collectively, a smart structure or a smart device). The illustratedpSKIN includes two sensors 215 and the actuator 310, but othercombinations of sensors/actuators are also possible. In someembodiments, the pSKIN 380 may be folded over an edge 360 of theaircraft structure 200. An integrated circuit (IC) chip 410 may beconnected to the connectors 225. In some embodiments, the IC chip 410may be bonded or soldered to the connectors 225. In some embodiments,the IC chip 410 is on the side of the aircraft structure 200. As aresult, the IC chip 410 and the connectors 225 may be better protectedagainst the environment, as explained with reference to FIGS. 4B-4Cbelow.

FIG. 4B shows an aircraft structure 200 a connected to another aircraftstructure 200 b. In some embodiments the aircraft structures 200 a, 200b may be segments of the aircraft wing or fuselage. In otherembodiments, the aircraft structures 200 a, 200 b may be segments of arotorcraft, e.g., segments of a helicopter propeller. Since theillustrated aircraft structures 200 a, 200 b butt against each other,the IC chip 410 and the connectors 225 are protected against theenvironment, e.g., rain or air drag. In some embodiments, conductivetraces 230 or other wiring can electrically connect the pSKIN 380 withelectronics (e.g., power supplies, controllers, etc.) away from theaircraft structure 200 a. For example, the power supplies, controllers,etc. may reside on the aircraft itself, but away from the structure 200a. In some embodiments, the pSKIN 380 may be wirelessly connected (e.g.,Bluetooth, WiFI, etc.) with external electronics.

FIG. 4C shows aircraft structures 200 a, 200 b, 200 c that are mutuallyconnected, and mounted on a stand 420 inside a wind tunnel 400. In someembodiments, the aircraft structure 200 a has its leading edge 350oriented to face an incoming airflow at velocity U. In some embodiments,the actuator 310 (e.g., a heater) may manipulate (e.g., heat up) theincoming air to change its physical properties. The downstream sensors215 (e.g., thermocouples or strain gauges) may measure some physicalproperties (e.g., temperature of air or drag force) that are influencedby the upstream actuator 310. In some embodiments, the pSKIN 380 may beused for, e.g., deicing or flow control. As explained with reference toFIGS. 4A and 4B, the IC chip 410 and/or the connectors 225 are lessexposed to the environmental force and degradation since they are not inthe path of the flow. In some embodiments, the conductive traces 230 (orother wired or wireless connections) may connect the pSKIN 380 withelectronics outside of the wind tunnel 400.

FIG. 5 is an exploded view of a pSKIN assembly 5800 in accordance withan embodiment of the presently disclosed technology. In someembodiments, the pSKIN assembly 5800 includes a pSKIN 580 having a foil580 a (e.g., a polymer, wax paper, thin PCB, etc.) with the 3D-printedelectronics and a layer of adhesive 580 b (e.g., an epoxy). Theillustrated pSKIN 580 is covered with a protective cover 510 having aprotective foil 510 a (e.g., a polymer) and a layer of adhesive 510 b.In some embodiments, the protective cover 510 and/or the pSKIN 580 canbe made by casting one-part epoxy resins onto a wax paper or olefinbased foils. In some embodiments, the foils 580 a/510 a may be rigidenough to handle, yet remain pliable enough to conform to many curvedsurfaces. The sensors/actuators (e.g., a heater 310), conductive traces230, and connectors 225 can be 3D-printed over the foil 580 a. In someembodiments, the sensors, actuators and/or electronics of the pSKIN 580may be made by lithography or screen printing. The combination of thepSKIN 580 and the protective cover 510 can be applied over the aircraftstructure 200. In some embodiments, in-situ curing can be used to curethe pSKIN assembly 5800 without affecting the aircraft/host structuresubstrate using, for example, photonic based curing, UV based curing,electromagnetic systems such as induction heating and microwaves, and/orthermal blankets. In at least some embodiments, the cured pSKIN assembly5800 retains good adhesion and functionality in presence of a hole 290(e.g., a rivet hole).

FIGS. 6A and 6B are plan and isometric views of an aircraft 6000 thatcarries sensors and actuators in accordance with an embodiment of thepresently disclosed technology. FIG. 6A is a plan view of the aircraft6000 that includes several sensors, actuators and power supplies (e.g.,batteries). Collectively, the aircraft 6000 and thesensors/actuators/electronics may be referred to as a smart structure ora smart device 6100. The aircraft 6000 may be, for example, an unmannedairplane, but other types of aircraft are also possible.

FIG. 6A shows an embodiment of the aircraft 6000 that carries severalsensors and actuators: thermocouples 610, ice sensors 620, sensors 215(e.g., strain sensors), and pressure sensors 105 (collectively, pSKIN orprinted multifunctional skin). Other numbers and arrangement of thesensors and actuators are also possible. In some embodiments, thesensors/actuators may be at least in part powered by batteries 630. Insome embodiments, the aircraft 6000 may include electronics (not shown)for digital or analog processing, wireless data transmission to groundor to another aircraft, etc. For example, the aircraft 6000 may includeheaters that are turned on and off based on the signal from the icesensors 620 that is processed by the on-board electronics. In otherembodiments, high-bandwidth pressure sensors can be coupled with ionicwind generators for boundary layer control. Furthermore, distributedsensors can be used to determine the position of streamwise vortices,and then surface electrodes for ionic wind may nudge or force thevortices back to their optimal location using a closed-loop controlsystem. As a result, more efficient aerodynamic vehicles with low skinfriction can be developed to, for example, reduce fuel consumption.

FIG. 6B shows the aircraft 6000 that has openings in the aircraft forhousing the sensors, actuators and power supplies. For example, in someembodiments, openings 105 h may be shaped and configured to receive thepressure sensors 105, and openings 630 h may be shaped and configured toreceive the batteries 630. Manufacturing of the openings 105 h, 630 h isdiscussed with reference to FIGS. 7A-7F below.

FIGS. 7A-7F are schematic views of equipping an aircraft structure withsensors and actuators in accordance with an embodiment of the presentlydisclosed technology. FIG. 7A schematically illustrates a step 7100 formanufacturing the aircraft structure 200. In some embodiments, a 3Dprinter 710 may eject a 3D material 720 (e.g., aerosols, powderedmetals, melted materials, polymer ceramic composites, etc.) that formthe aircraft structure 200. The 3D printer 710 may be controlled by acontroller or a computer (not shown).

FIG. 7B schematically illustrates a step 7200 for manufacturing theaircraft structure 200. In the step 7200, an opening 730 (e.g., a pocketor a housing, also referred to as a first opening) is created forhousing the electronics for sensors/actuators.

FIG. 7C schematically illustrates a step 7300 for manufacturing theaircraft structure 200. In the step 7300, an electronics printer 740(also referred to as “3D electronics printer” or “additive electronicsprinter” or “direct write electronics printer”) prints electronics 750 afor supporting the sensors/actuators. The electronics printer 740 placesa functional material 745 on the surface the electronics 750 a. Activeand passive elements may be placed directly on the surface or inside thepockets of the aircraft structure 200. In some embodiments, theelectronics printer 740 can directly deposit a range of commercial andcustom electronic materials such as resistors, conductors (copper,silver, gold, etc.), dielectrics, piezoelectrics, carbon nanotubes,adhesives, polymers, and other materials. Using these materials,different sensors, resistors, capacitors, transducers, interconnects,coils, active circuit elements, and/or antennas may be fabricated overthe aircraft structure 200. In some embodiments, electronics 750 b mayalso be printed in-situ or may be pre-made using a 3D printer orconventional methods (e.g., surface mount technologies).

FIG. 7D schematically illustrates a step 7400 for manufacturing theaircraft structure 200. In the step 7400, a buildup of the aircraftstructure 200 continues using the 3D printer 710. In some embodiments,the electronics 750 a/750 b may become encapsulated in the 3D material720, leaving openings 760 for accessing the electronics 750 a/750 b.

FIG. 7E schematically illustrates a step 7500 for manufacturing theaircraft structure 200. In the step 7500, a wiring 770 may be added bythe electronics printer 740. In some embodiments, the 3D printer 710 mayprint conductive materials, e.g., the wiring 770 inside the openings 760(also referred to as second openings). In some embodiments, the wiring770 may connect the electronics 750 a/750 b to the surface of theaircraft structure 200.

FIG. 7F schematically illustrates a step 7600 for manufacturing theaircraft structure 200. In the step 7600, the electronics printer 740may add, for example, the pressure sensor 105, the temperature sensor110 and the strain sensor 115 to the surface of the aircraft structure200. In other embodiments, different combinations of thesensors/actuators may be added by the electronics printer 740, forexample, the pSKIN 580 may combine thermistor-based temperature sensors,strain gauges, and pressure sensors. Generally, the sensors/actuatorsare relatively thin in comparison to the aircraft structure 200. Forexample, in some embodiments, the sensors/actuators may be less than 10μm, less than 100 μm, or less than 2 mm thick. In some embodiments, thewiring 770 connect the electronics 750 a/750 b with thesensors/actuators of the pSKIN 580.

FIG. 8 is an isometric view of printing sensors and actuators over theaircraft 6000 with in accordance with an embodiment of the presentlydisclosed technology. In some embodiments, the electronics printer 740may be positioned above the aircraft 6000, and may be driven by acomputer controlled positioning system (not shown). In some embodiments,the electronics printer 740 may use different functional material forprinting different components of the pSKIN (e.g., the functionalmaterial for the conductive traces 230 and dielectric-based ink for theinsulation of the ice sensor 620). Some embodiments of the sensors thatare manufacturable by the electronics printer 740 are temperaturesensors, strain sensors, static or low frequency pressure sensors, forcesensitive resistors, dynamic or high frequency pressure sensors, heatflux sensors, negative pressure or vacuum sensors, piezoelectricsensors, vibration sensors, impact sensors, airflow sensors, acousticsensors, electric field sensors, antennas, magnetic field sensors, crackdetection sensors, ice sensors, sensors detecting other characteristicsrelating to flight, sensors detecting other characteristics of theenvironment, sensors detecting other characteristics relating toaircraft structural health, and a metamaterial with an orderedone-dimensional, two-dimensional or three-dimensional structure. Someembodiments of the actuators that are manufacturable by the electronicsprinter 740 are: ice remediation heaters, ion actuators, plasmaactuators, piezoelectric transducers, aircraft controls, and otherplanar functional devices printed or adhered to the surface of theaerodynamic structure.

Electronics Printer

In some embodiments, an OPTOMEC Aerosol Jet (AJ) system can be used asthe electronics printer 740. The pSKIN sensors/actuators may be printeddirectly on metallic structures, other 3D printed structures, and othersuitable substrates such as composites. Some examples of functionalmaterial 745 are: carbon nanotube inks, conductors (e.g., metals),insulators, semiconductors, semimetals, resistors, dielectrics,adhesives, epoxies, filled epoxies, polymers, filled polymers,elastomers, filled elastomers, ceramic particulates, piezoelectricmaterials, magnetic materials, functional materials, graphene inks,biological materials, and composites of these material.

Printed Strain Gauge Sensors

In some embodiments, the strain sensor (strain gauge) 115 can be printedover different substrates (e.g., aircraft structure 200): glass,polyimide, composite materials, ceramics, and anodized aluminum 2024 T3.The functional materials 745 may include metals, elastomers,piezolectrics, PARU silver nano ink, Heraeus PEDOT:PSS 1000 and BrewerScience Carbon Nano Tube (CNT) inks. In some embodiments, the electricalresistance for the functional material 745 is between 100Ω and 350Ω forParu silver, around 200 kΩ for CNTs and between 0.4MΩ and 0.6MΩ forPEDOT:PSS. Since aluminum is conductive, several layers of Sigma Aldrichpolyimide may be printed onto the aluminum aircraft structure 200 priorto the conductive ink application. In some embodiments, the strainsensors (strain gauges) can be printed in about 10 layers with a totalprint time of about 60 minutes at 4 mm/s translations.

Printed Temperature Sensors

In some embodiments, the temperature sensors 110 are thermocouples orthermistors. Conventional manufacturing of the thermocouples requires anoxygen free atmosphere and high curing temperatures. In some embodimentsof the present technology, a low-temperature curing process for thethermocouples can be used by having the functional material thatrequires low processing temperature conditions.

In some embodiments, the thermistors can be made of semiconductingmixtures of oxides of transition metals with low processing temperatureconditions (e.g., silicon based silistors, switching type materials, orgraphite). In some embodiments, these materials may be solvable in asolvent to produce the functional material 745. In one embodiment, thefunctional material 745 may include Molybdenum Disulphide (MoS2) andMolybdenum Disulphide (MoS2) diluted 1:1 with Toluene (polar solvent),to lower viscosity and to facilitate printing. In other embodiments, thefunctional material 745 may include Molybdenum Disulphide (MoS2),Magnetite, and poly polystyrene sulfonate (PEDOT:PSS).

Printed Pressure Sensors

In some embodiments, the sensors may include printed pressure sensors105, for example, Force Sensitive Capacitors (FSCs), Force SensitiveResistors (FSRs), and/or Lead Zirconate Titanate (PZT) sensors. In anembodiment, the FSC can operate by continuously evaluating a capacitanceof a printed capacitor having two parallel conductive plates separatedby a dielectric material. The capacitance of the capacitor may bymodeled by the equation C=kεA/D, where k is the permittivity of thedielectric between the plates, ε is the permittivity of space, A is thearea of the capacitor, and D is the thickness of the dielectric. Byprinting these sensors using appropriate functional materials 745, theconductor plates and dielectric material can be made relatively thin,increasing the static capacitance of the sensor. In some embodiments,the printed conductor plates/dielectric material may have the thicknessof about 100 nm to 30 μm. In some embodiments, PARU silver nano ink canbe used as the conductive material, and Sigma Aldrich polyimide as thedielectric layer.

In some embodiments, the sensors (e.g., pressure sensors) may bemanufactured by sintering micro-scale lead zirconate titanate (PZT)films with relatively low substrate temperature increases. In otherembodiments, the functional material 745 may include ink formulated fromPZT nanoparticles, solvent, dispersant and adhesion promoter. In someembodiments, the inks may dry for a few hours (e.g., two hours) in avacuum at about 200° C. In some embodiments, the functional material 745may be photonically sintered using sub-millisecond pulses of broadspectrum light. In some embodiments, the remanent polarization andcoercive field for thermally sintered PZT film were 16.1 μC/cm2 and 4.3kV/cm, respectively. For the photonically sintered materials, theremanent polarization can be 27.7 μC/cm2 and coercive field can be 3.1kV/cm. The piezoelectric voltage constants (g31) for the two film groupscan be −5.0×10−3 V-m/N (for thermally sintered functional material) and−5.5×10−3 Vm/N (for photonically sintered functional material). For atleast some embodiments, the foregoing values indicate that the PZT filmswere successfully sintered. In some embodiments, to avoid the relativelyhigh temperature of sintering the conventional PZT material, a colloidalbased functional material 745 may be used. As a result, instead ofconventional sintering at about 600° C., the curing and sintering of thePZT particles in the functional material 745 may occur in a temperaturerange of 150-200° C., therefore being suitable for direct printing overmany metallic and non-metallic aircraft structures 200.

FIG. 9 is an isometric view of a wind tunnel testing of sensors andactuators in accordance with an embodiment of the presently disclosedtechnology. In the illustrated embodiments, the aircraft 100 carries thesensor 310 (e.g., a heater) and the sensor 215 (collectively, pSKIN).The aircraft 100 is mounted on the stand 420, and oriented to face theincoming airflow at velocity U. In some embodiments, thesensors/actuators of the pSKIN may make measurements and/or manipulatethe fluid flow to, for example, improve flight characteristics of theaircraft 100.

FIGS. 10A and 10B are graphs of load measurements in accordance with anembodiment of the presently disclosed technology. In particular, FIG.10A is a graph of the load over time, and FIG. 10B is a graph of themeasured load over time. The horizontal axes for both graphs are time inseconds.

The vertical axis of the graph in FIG. 10A corresponds to applied loadin lbF. In the illustrated embodiment, the applied load increases overthe time, reaches a peak of about 250 lbF after about 19 seconds, andthen decreases to about 25 lbF after 25 seconds. In some embodiments,the load may be applied over an aircraft structure (e.g., a wing of anaircraft).

The vertical axis of the graph in FIG. 10B corresponds to the resistancein Ω of a strain sensor (e.g., the strain sensor 115 placed over anaircraft wing). The behavior of the measured resistance in Ω in FIG. 10Bgenerally corresponds to the loading shown in FIG. 10A, i.e., the shape,maximum, and minimum of the graph in FIG. 10B generally follows theshape of graph in FIG. 10A, therefore indicating a generally linearresponse of the strain sensor. In at least some embodiments, a linearresponse of a sensor is a preferred response.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustration,but that various modifications may be made without deviating from thedisclosure. Moreover, while various advantages and features associatedwith certain embodiments have been described above in the context ofthose embodiments, other embodiments may also exhibit such advantagesand/or features, and not all embodiments need necessarily exhibit suchadvantages and/or features to fall within the scope of the technology.For example, ice protection systems can be printed next to temperaturesensor arrays for de-icing/anti-icing. In some embodiments, thepSKIN-based control of the aerodynamics/hydrodynamics of the vehiclesmay result in improved performance of the vehicles. Accordingly, thedisclosure can encompass other embodiments not expressly shown ordescribed herein.

The embodiments of the invention in which an exclusive property orprivilege is claims are defined as follows:
 1. A method of instrumentingan aerodynamic structure, comprising: providing the aerodynamicstructure having a first surface exposed to an outside environment; andforming a printed multifunctional skin (pSKIN) by printing at least asensor, an actuator and a conductive trace over the first surface of theaerodynamic structure by additive manufacturing.
 2. The method of claim1, further comprising: applying a protective cover over the pSKIN. 3.The method of claim 1, wherein the first surface of the aerodynamicstructure has a hole, the method further comprising: sealing the holewith the pSKIN.
 4. The method of claim 1, wherein the aerodynamicstructure is an element of a pump, a wind turbine, an air fan, asubmarine, a ship, an engine, a prosthetics, or an aircraft.
 5. Themethod of claim 1, wherein the aerodynamic structure is an unmannedvehicle.
 6. The method of claim 1, wherein the sensor is an electricfield sensor, an antenna, or a magnetic field sensor.
 7. An instrumentedaerodynamic structure, comprising: the aerodynamic structure having afirst surface exposed to an outside environment; and a printedmultifunctional skin (pSKIN) comprising a sensor, an actuator and aconductive trace, wherein the pSKIN is produced by additivemanufacturing, and wherein the pSKIN is applied over the surface of theaerodynamic structure.
 8. The structure of claim 7, wherein the firstsurface of the aerodynamic structure has a hole, and wherein the pSKINseals the hole.
 9. The structure of claim 7, wherein the aerodynamicstructure is an element of a pump, a wind turbine, an air fan, asubmarine, a ship, an engine, a prosthetics, or an aircraft.
 10. Thestructure of claim 7, wherein the aerodynamic structure is an unmannedvehicle.
 11. The structure of claim 7, wherein the sensor is an electricfield sensor, an antenna, or a magnetic field sensor.
 12. A method ofmanufacturing an aircraft structure, comprising: providing a firstaerodynamic structure having a first surface exposed to an outsideenvironment, and a second surface facing a second aerodynamic structure;printing a sensor over the first surface of the first aerodynamicstructure; printing conductive traces over the first surface of thefirst aerodynamic structure, wherein the conductive traces electricallyconnect the sensor to electronics; and protecting the electronicsagainst environment by attaching the second aerodynamic structure to thefirst aerodynamic structure, wherein the second aerodynamic structurehas a third surface exposed to the outside environment, and a fourthsurface facing the first aerodynamic structure, and wherein theelectronics are housed between the second surface of the firstaerodynamic structure and the fourth surface of the second aerodynamicstructure.
 13. The method of claim 12, further comprising: placing anactuator over the first surface of the first aerodynamic structure; andelectrically connecting the actuator to the electronics with theconductive traces.
 14. The method of claim 12, wherein the aircraftstructure is an element of a pump, a wind turbine, an air fan, asubmarine, a ship, an engine, a prosthetics, or a pipeline.
 15. Themethod of claim 12, further comprising: printing the sensor by anelectronics printer.
 16. The method of claim 13, further comprising:printing the sensor and the actuator over a foil by an electronicsprinter using additive manufacturing; and adhering the foil to the firstsurface of the first aerodynamic structure.
 17. The method of claim 13,wherein the sensor and the actuator are less than 100 μm thick.
 18. Anaircraft structure, comprising: a first aerodynamic structure having afirst surface exposed to an outside environment, and a second surfacefacing a second aerodynamic structure; and a printed sensor carried bythe first surface of the first aerodynamic structure; at least oneprinted conductive trace over the first surface of the first aerodynamicstructure; a second aerodynamic structure having a third surface exposedto the outside environment, and a fourth surface facing second surfaceof the first aerodynamic structure; and electronics connected to theprinted sensor through the at least one printed conductive trace,wherein the electronics is configured and protected in a space betweenthe second surface of the first aerodynamic structure and the fourthsurface of the second aerodynamic structure.
 19. The structure of claim18, further comprising a printed actuator carried by the first surfaceof the first aerodynamic structure.
 20. The structure of claim 19,wherein the actuator is a heater at a leading edge of the aircraftstructure, and the printed sensor is a strain sensor downstream from theprinted actuator.
 21. The structure of claim 18, wherein the aerodynamicstructure is an aircraft structure.
 22. The structure of claim 18,wherein the aerodynamic structure is an element of a pump, a windturbine, an air fan, a submarine, a ship, an engine, a prosthetics, or apipeline.
 23. The structure of claim 18, wherein the aircraft structureis an unmanned airplane.
 24. The structure of claim 17, wherein theprinted sensor is less than 10 μm thick.
 25. The structure of claim 17,wherein the printed sensor and the printed actuator are less than 100 μmthick.
 26. The structure of claim 17, further comprising: an adhesivelayer attached to the outer surface of the aerodynamic structure; and afoil attached to the adhesive layer, wherein the foil carries theprinted sensor and the printed actuator.